[time-nuts] Sub Pico Second Phase logger

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 10 19:58:49 EST 2008


Joseph M Gwinn wrote:
> Bruce,
>
>
> time-nuts-bounces at febo.com wrote on 12/10/2008 04:46:50 PM:
>
>   
>> Joe
>>
>> Another limitation on using too low a beat frequency is imposed by the
>> increasing equivalent input noise spectral density of the sound card as
>> the frequency decreases.
>>     
>
> Yes, although people made good use of 1 Hz in DMTD instruments despite the 
> junk near DC.
>
>
> Joe
>   
Joe

The low frequency noise of the components used in their unoptimised
slope amplifiers is significantly smaller than that of a sound card.
A Collin's style optimised slope amplifier limiter may be useful for use
with a sound card (particularly the lower resolution ones) if one is
timetagging the beat frequency zero crossings.
Less slope gain will be required than when driving a counter input.
In the flicker noise region choice of beat frequency is relatively non
critical.

Bruce




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